Abstract
The extracellular phytase produced by the Bacillus amyloliquefaciens US573 strain, isolated from geothermal soil located in Southern Tunisia was purified and characterized. This calcium-dependent and bile-stable enzyme (PHY US573) was optimally active at pH 7.5 and 70 °C. It showed a good stability at pH ranging from 4 to 10, and especially, an exceptional thermostability as it recovered 50 and 62% of activity after heating for 10 min at 100 and 90 °C, respectively. In addition, PHY US573 was found to be extremely salt-tolerant since it preserved 80 and 95% of activity in the presence of 20 g/l of NaCl and LiCl, respectively. The gene corresponding to PHY US573 was cloned. It encodes a 383 amino acids polypeptide exhibiting 99% identity with the highly thermostable phytases from Bacillus sp. MD2 and B. amyloliquefaciens DS11 (3 and 5 residues difference, respectively), suggesting the existence of common molecular determinants responsible for their remarkable heat stability. Overall, our findings illustrated that in addition to its high potential for application in feed industry, the salt tolerance of the PHY US573 phytase, may represent an exciting new avenue for improvement of phosphorus-use efficiency of salt-tolerant plants in soils with high salt and phytate content.